This invention relates to apparatus for marking flat sheets of material and, in particular, to apparatus for rapidly laying out bend lines upon sheets of material so that the sheets can be accurately worked in a brake.
When bending sheets of material into various geometric shapes or configurations, it is the common practice in the art to first lay out or mark the bend lines on the surface of the sheet prior to loading the sheet in the brake. The bend lines provide a visual means by which the operator can properly align the sheets in the brake. Heretofore bend lines were typically located from some key datum plane or planes and initially marked by forming a series of dimple-like marks along the plane of the line using a prick punch. A straight edge was then aligned along the punch marks and a line marked using a scribing tool. When a small number of sheets were to be formed, each sheet was individually laid out by hand using a scale to determine the key points. As can be seen, this type of work is rather time consuming and tedious. Furthermore, because all of the numerous steps must be performed by hand, there is a high probability that one or more of the layouts will be inaccurate and the part fabricated therefrom will eventually have to be scrapped.
When a large number of similar sheets are to be fabricated, punch hole templates are usually constructed having guide holes formed therein for accurately locating and guiding the punch. The template is placed over the working surface of the sheet and is accurately located from a pair of edges so that the guide holes are accurately positioned over the sheet. After the punched holes have been formed, the template is removed from the sheet and the bend lines scribed using a straight edge and a marking tool. Here again, a large number of operations must be performed by hand using a variety of different tools. Accordingly, the accuracy of the layout is to a large extent still dependent upon the skill of the layout person.
The laying out of complex sheet metal forms often times further requires that both the front and back surfaces of the sheet be marked and the bend lines contained on the opposing surfaces be accurately located in relation to each other. This task is sometimes extremely difficult to carry out, particularly when the sheets are laid out on a flat horizontal working surface. As can be seen, the layout person is not readily able to relate a bend line on the top side of the sheet with one formed on the opposite or bottom side. As a consequence, even with the use of one or more templates, the process includes a number of different steps which provide considerable room for error.
As evidenced by U.S. Pat. Nos. 3,113,382 and 4,208,799, various types of apparatus have been developed which aid in the marking and cutting of sheet metal panels used for siding houses. However, these devices do not overcome the difficulties encountered when laying out flat sheets of bendable materials as noted above. U.S. Pat. No. 1,521,544 describes a carpenter's tool that can be adjusted to mark joint lines in timbers prior to the joints being cut. This device, however, is not adaptable for use in conjunction with thin sheets of materials to permit the accurate laying out of bend lines on the sheets of material.